1. Field of the Invention
This invention relates to a biaxially oriented laminate polyester film. More specifically, it relates to a biaxially oriented laminate polyester film useful for a magnetic tape, particularly a digital recording magnetic tape, having stable running properties and excellent magnetic output characteristics.
2. Description of the Related Art
JP-A 2-77431 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") discloses a biaxially oriented laminate polyester film having a specific relationship between the thickness of a polyester layer and the particle diameter of fine particles contained in the polyester layer.
In recent years, a large number of digital recording magnetic tapes have been made available and the thickness of a magnetic layer or a back coated layer has been further reduced to cut down the production costs of a magnetic tape. Due to the reduction in thickness, the surface properties of the magnetic tape is much more affected by the surface properties of a base film than before.
The magnetic tape runs through a complicated running system at the time of recording or reproduction in most of its systems. If the running properties of the magnetic tape are not balanced at a contact portion of the surface of a magnetic layer or back coated layer, such a defect as a track deviation or the like occurs. For example, in a DLT (digital linear tape), when the running properties of the tape are not balanced at a contact portion of the surface of a magnetic layer or back coated layer, a defect called "LTM (lateral tape motion)" occurs.
It is an object of the present invention to provide a biaxially oriented polyester film which overcomes the above problem, has stable running properties when a magnetic tape is formed therefrom, and is useful as a base film for a magnetic tape having a high S/N (signal/noise) ratio (may be also referred to as "excellent output characteristics" hereinafter).
It is another object of the present invention to provide a magnetic tape which comprises the above film of the present invention as a base film.
Other objects and advantages of the present invention will become apparent from the following description.